In the investment casting of such articles as turbine blades or vanes which are hollow for cooling purpose, one main problem is to have the core, that forms the internal passages in the cast article, precisely located so as to assure a satisfactory completed cast article that can be adequately cooled. When the article is cast in a single piece involved techniques are required to inspect the finished article to determine the wall thickness or the precise location and dimensions of the internal passages. If these articles are for use in high performance gas turbine engines in aircraft, imprecision in the location of the cooling passages may cause premature blade or vane failure. The removal of the core from the finished casting may present certain difficulties since leaching techniques are required.
The copending application of Hayes et al, Ser. No. 416,563 filed Nov. 16, 1973, overcomes the inspection problem by making the mold of a precast strong-back central mold element, with opposed precast outer mold elements mounted on opposite sides of the central element. Since these three elements are made separately, careful inspection of these parts before mold assembly is possible. Further, since the vane or blade is made in opposed halves by this technique, these completed halves may also be completely inspected especially on their inner surfaces prior to bonding the opposed halves together. This arrangement is most workable but is expensive unless the cost of the mold devices by which the precast mold elements are formed can be spread over a large production run of the articles desired.